This application relates to a new class of homo and copolymers having properties which make them especially useful as photoresists, especially in view of their very high resistance to oxygen reactive ion etching (O.sub.2 -RIE).
U.S. Pat. Nos. 4,587,205 and 4,588,801 to Zeigler et al describe polysilane polymers useful as self-developing photoresist materials, as well as methods for their use in microlithography and other high resolution imaging applications. These are the pioneer patents in the polysilane field. A major factor for the high level of interest generated by the inventions of these patents, in addition to their self-developing capabilities, is the very high resistance to O.sub.2 -RIE of the materials. They etch about 30 times slower than standard positive-working photoresists under the same conditions.
O.sub.2 -RIE resistance allows the combining in a single layer of these materials of the functions normally provided in two layers in trilayer or, more generally, multilayer lithography. Thus, a single layer of self-developing polysilane can be used to combine the functions of the imaging layer and the etch barrier layer in conventional methods. Trilayer lithography can be converted as a result into bilayer lithography using the potential of the photovolatilizing polysilanes. This simplification allows the numbers of steps necessary to carry out multilayer lithography to be cut essentially in half, with attendant reductions in cost and pollutant emissions and increases in device yield. As the topography of integrated circuits becomes even greater at smaller critical device dimensions, multilayer lithographic schemes become increasingly necessary to print the submicron features present in the state-of-the-art VLSI circuits. Thus, the importance of self-developing polysilanes is proportionately increased.
The smallest feature that can be transferred to, e.g., a silicon wafer by bilayer lithography is closely related to the ratio of the etch rate of the underlying planarizing layer to that of the imaging layer; the higher this ratio is, the smaller the feature printed in the imaging layer that can be transferred without unacceptable loss of feature resolution. Even though the polysilanes of the prior art have very high etch rate ratios, materials exhibiting even higher ratios are much desired.